Solid state light emitting devices such as light emitting diodes (LEDs) and solid state lasers are used in a wide range of applications from conventional lighting systems to optical communication systems. In particular, nitride based LEDs enable the use of LEDs for general lighting purposes. However, emission efficiency for such devices drops considerably for wavelengths above 480 nm. A way to compensate this is to use blue emitting LEDs in such a way that part of the emitted blue light is converted to green-yellow light by interaction with a phosphorescent material. However, phosphorescent conversion suffers from several conversion loss mechanisms during the transition from a higher energy radiation to lower energy radiation resulting in limited conversion efficiency while also the emission peak shape is broadened. Therefore, LEDs emitting directly in the green to red parts of the visible spectrum would provide considerable benefits such as eliminated conversion losses and improved color tunability.
For example, gallium nitride (GaN) based light sources can be adapted to shift the emission wavelength towards the red end of the visible spectrum. WO2008/078297 discloses a method for manufacturing a GaN-based semiconductor light emitting device configured to emit multiple wavelengths of light. This is achieved by forming a plurality of posts from a mask layer having a plurality of openings, where each post comprises a light emitting layer disposed between an n-type and a p-type region. The emitted wavelength is controlled by the diameter of the post.